The File List lists the pdf file(s) which were are added to the PDF Image Extracto. It shows the number of the raster
images contained in the files, and controls if the images from the correspondent file are displayed in the
Preview area.

Click on the check box to the left of the file name to add all the images from this file the the Preview Area.

Alternatively,
click on the Show/Hide Image Preview button.

Select All button selects all the files in the list, while Unselect button
unselects all the selected files.